Research On Seismic Performance Of Reinforced Concrete Beam Bridge Based On Material Degradation

Reinforced concrete bridges constitute a considerable proportion in our country.After the operation of concrete structures under the natural environment and service conditions they have undergone long-term alternate changes in temperature and humidity between day and night,as well as physical and chemical corrosion of harmful substances in the surrounding water medium,resulting in deterioration of the external and internal material properties and different degrees of cracking and damage.Therefore,in actual service,there must be some damage due to insufficient durability of piers,which often leads to the degradation of the bearing capacity of piers and the decline of their ability to resist natural disasters such as earthquakes.In this paper,the influence of material performance degradation on seismic performance of bridge structure is analyzed,which can provide theoretical basis for bridge life-cycle design,operation of existing bridges and seismic performance evaluation.This paper mainly carries out the following research:(1)To study the deterioration factors of reinforced concrete structure materials,firstly,the deterioration factors of materials are analyzed,and then the relationship between the deterioration of structural material properties and the time under the action of single and double factors,such as carbonization,freeze-thaw and chloride ion,is summarized respectively.The material degradation model of reinforced concrete is obtained,and the material properties parameters of the structure are calculated with service time.(2)The FE model of bridge pier and column is established by OpenSees software.Considering the spatial variability of material degradation,2000 material samples are sampled by Latin super-vertical sampling method for monotonic loading and hysteretic analysis.Finally,the hysteretic energy dissipation,backbone curve,stiffness degradation and ductility of the sampled statistic values in different time periods are analyzed.(3)A 3-span reinforced concrete beam bridge model is established by using FE software ANSYS.Based on the influence of various factors of material deterioration in Chapter 2,the nonlinear time-history analysis of the structure under uniform excitation of seismic load is carried out,and the seismic performance of the reinforced concrete bridge is evaluated in the whole life time under seismic action.The calculation results show that the bridge structure is in dangerous period after 75 years of service,and the ability of resisting earthquake decreases more obviously.Itis necessary to carry out scientific quantitative detection in time and reinforce and repair regularly in order to ensure the safety performance of the bridge during its service life.(4)Considering the randomness of earthquake ground motion,seismic vulnerability analysis of reinforced concrete bridge piers and columns is carried out based on IDA vulnerability analysis method.Twenty seismic records are selected to conduct time history analysis of piers and columns,while the damage index and the state limit value of it were define.Then the IDA analysis of bridge piers and columns was carried out to obtain the probabilistic seismic demand model and finally form the vulnerability curve.The vulnerability curves of bridge piers and columns in different service periods and under different failure limit states were compared and analyzed.The results show that the performance deterioration degree of the reinforced concrete material lower slightly,whilst the probability of serious damage to the pier and column is small in the initial stage of the bridge.And the change of the seismic capacity is small.With the bridge service time increasing,the mechanical properties of the reinforced concrete material gradually degenerate,which makes the seismic ability of the structure to withstand seismic action decrease and the probability of damage gradually increase.